WO2016013882A1

WO2016013882A1 - Method and apparatus for transmitting channel state information in wireless access system

Info

Publication number: WO2016013882A1
Application number: PCT/KR2015/007668
Authority: WO
Inventors: 김형태; 박종현; 김기준
Original assignee: 엘지전자 주식회사
Priority date: 2014-07-23
Filing date: 2015-07-23
Publication date: 2016-01-28
Also published as: KR20170002404A; US10547356B2; JP6518268B2; KR102014797B1; US20170195017A1; EP3174218A4; CN106537809A; EP3174218A1; CN106537809B; AU2015294786B2; AU2015294786A1; JP2017522768A

Abstract

A method for a terminal transmitting channel state information (CSI) in a wireless access system that supports massive multiple-input multiple-output (MIMO) according to one embodiment of the present invention may comprise the steps of: receiving CSI configuration information for reporting CSI; and transmitting CSI and identification information with respect to the partial channel corresponding to the CSI of the full channel according to the massive MIMO, on the basis of the CSI configuration information.

Description

Method and apparatus for transmitting channel state information in wireless access system

The present invention relates to a wireless communication system, and more particularly, to a method of transmitting channel state information in a wireless access system supporting massive multiple input multiple output (MIMO) and an apparatus for supporting the same.

Multi-Input Multi-Output (MIMO) is a technology that improves the transmission and reception efficiency of data by using multiple transmission antennas and multiple reception antennas, instead of using one transmission antenna and one reception antenna. Using a single antenna, the receiving side receives data through a single antenna path, but using multiple antennas, the receiving end receives data through multiple paths. Therefore, the data transmission speed and the transmission amount can be improved, and the coverage can be increased.

Single-cell MIMO operation is a single user-MIMO (SU-MIMO) scheme in which one terminal receives a downlink signal in one cell and two or more terminals are downlinked in one cell. It can be divided into a multi-user-MIMO (MU-MIMO) scheme for receiving a link signal.

Channel estimation refers to a process of restoring a received signal by compensating for distortion of a signal caused by fading. Here, fading refers to a phenomenon in which the strength of a signal is rapidly changed due to multipath-time delay in a wireless communication system environment. For channel estimation, a reference signal known to both the transmitter and the receiver is required. In addition, the reference signal may simply be referred to as a reference signal (RS) or a pilot according to the applied standard.

The downlink reference signal is a coherent such as a Physical Downlink Shared CHannel (PDSCH), a Physical Control Format Indicator CHannel (PCFICH), a Physical Hybrid Indicator CHannel (PHICH), and a Physical Downlink Control CHannel (PDCCH). Pilot signal for demodulation. The downlink reference signal includes a common reference signal (CRS) shared by all terminals in a cell and a dedicated reference signal (DRS) only for a specific terminal. LTE-based systems with extended antenna configurations (e.g., LTE-supporting 8 transmit antennas) compared to conventional communication systems supporting 4 transmit antennas (e.g., according to the

LTE release

8 or 9 standard). In the system according to A standard, DRS-based data demodulation is considered to support efficient reference signal operation and advanced transmission scheme. That is, DRSs for two or more layers may be defined to support data transmission through an extended antenna. Since the DRS is precoded by the same precoder as the data, it is possible to easily estimate channel information for demodulating the data at the receiver without additional precoding information.

Meanwhile, while the downlink receiving side can obtain precoded channel information for the extended antenna configuration through the DRS, a separate reference signal other than the DRS is required to obtain uncoded channel information. Accordingly, in the system according to the LTE-A standard, a reference signal for acquiring channel state information (CSI) may be defined at the receiving side, that is, CSI-RS.

Based on the above discussion, a method and apparatus for transmitting channel state information in a wireless access system supporting massive MIMO (Massive Multiple Input Multiple Output) are proposed.

Technical problems to be achieved in the present invention are not limited to the above technical problems, and other technical problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

In order to solve the above problem, in a method of transmitting a channel state information (CSI) by the terminal in a wireless access system that supports Massive Multiple Input Multiple Output (MIMO) according to an embodiment of the present invention, CSI reporting Receiving CSI configuration information for the device; And transmitting identification information on the partial channel corresponding to the CSI among the CSI and all the channels according to the massive MIMO based on the CSI configuration information.

The partial channel corresponds to the antenna of the first column of the antenna array according to the massive MIMO when the identification information is the first value, and the partial channel corresponds to the first row of the antenna array according to the massive MIMO when the identification information is the second value. It can correspond to the antenna of.

The partial channel may be associated with a single codebook when the identification information is a first value, and the partial channel may be associated with a dual codebook when the identification information is a second value.

When the identification information is the first value, the partial channel indicates that the ratio of the feedback frequency of the first partial channel and the second partial channel has a first ratio value, and when the identification information is the second value, the partial channel is set to the first value. It may indicate that the ratio of the feedback frequency of the first partial channel and the second partial channel has a second ratio value.

The identification information may be transmitted together with the CSI only when the CSI is a wideband PMI (Precoding Matrix Indicator), and may not be transmitted together when the CSI is a narrowband PMI.

The identification information is fed back together with a rank indicator (RI), and a PMI (Precoding Matrix Indicator) corresponding to the same partial channel may be transmitted until the updated identification information is transmitted together with the RI.

The partial channel information may include a partial CSI indicator (PCI).

A terminal for transmitting channel state information (CSI) in a wireless access system supporting Massive Multiple Input Multiple Output (MIMO), according to another embodiment of the present invention, comprising: a radio frequency (RF) unit; And a processor, wherein the processor is configured to receive CSI configuration information for CSI reporting, and to identify identification information of a partial channel corresponding to the CSI among all channels according to the CSI and the massive MIMO based on the CSI configuration information. Can be configured to transmit.

The partial channel information may include a partial CSI indicator (PCI).

According to an embodiment of the present invention, a method for transmitting channel state information and a device supporting the same in a wireless access system supporting massive MIMO (Massive Multiple Input Multiple Output) can be provided.

Effects obtained in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide an embodiment of the present invention and together with the description, illustrate the technical idea of the present invention.

1 is a diagram illustrating a structure of a downlink radio frame.

2 is an exemplary diagram illustrating an example of a resource grid for one downlink slot.

3 is a diagram illustrating a structure of a downlink subframe.

4 is a diagram illustrating a structure of an uplink subframe.

5 is a configuration diagram of a wireless communication system having multiple antennas.

6 is a diagram illustrating a pattern of a conventional CRS and DRS.

7 is a diagram illustrating an example of a DM RS pattern.

8 is a diagram illustrating examples of a CSI-RS pattern.

9 is a diagram for explaining an example of a method in which a CSI-RS is periodically transmitted.

10 is a diagram for explaining an example of a method in which a CSI-RS is transmitted aperiodically.

FIG. 11 is a diagram for explaining an example in which two CSI-RS configurations are used.

12 shows an example of a 64 port 2D-AAS antenna arrangement.

13 shows an example of a cross-polarized (X-pol) antenna array AA.

14 is an illustration of an A / B block in X-pol AA.

15 to 23 are examples of a feedback method according to an embodiment of the present invention.

24 is a flowchart showing an example of an embodiment of the present invention.

25 is a diagram illustrating a configuration of a base station and a terminal that can be applied to an embodiment of the present invention.

The following embodiments combine the components and features of the present invention in a predetermined form. Each component or feature may be considered to be optional unless otherwise stated. Each component or feature may be embodied in a form that is not combined with other components or features. In addition, some components and / or features may be combined to form an embodiment of the present invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment.

In the present specification, embodiments of the present invention will be described based on a relationship between data transmission and reception between a base station and a terminal. Here, the base station has a meaning as a terminal node of the network that directly communicates with the terminal. The specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases.

That is, it is obvious that various operations performed for communication with a terminal in a network composed of a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A 'base station (BS)' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point (AP), and the like. The repeater may be replaced by terms such as relay node (RN) and relay station (RS). In addition, the term “terminal” may be replaced with terms such as a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), a subscriber station (SS), and the like.

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802 system, 3GPP system, 3GPP LTE and LTE-Advanced (LTE-A) system and 3GPP2 system. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various radio access systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (WirelessMAN-OFDMA Reference System) and the advanced IEEE 802.16m standard (WirelessMAN-OFDMA Advanced system). For clarity, the following description focuses on the 3GPP LTE and LTE-A standards, but the technical spirit of the present invention is not limited thereto.

A structure of a downlink radio frame will be described with reference to FIG. 1.

In a cellular OFDM wireless packet communication system, uplink / downlink data packet transmission is performed in subframe units, and one subframe is defined as a predetermined time interval including a plurality of OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame structure applicable to frequency division duplex (FDD) and a type 2 radio frame structure applicable to time division duplex (TDD).

1 is a diagram illustrating a structure of a type 1 radio frame. The downlink radio frame consists of 10 subframes, and one subframe consists of two slots in the time domain. The time it takes for one subframe to be transmitted is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms. One slot includes a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. In the 3GPP LTE system, since OFDMA is used in downlink, an OFDM symbol represents one symbol period. An OFDM symbol may also be referred to as an SC-FDMA symbol or symbol period. A resource block (RB) is a resource allocation unit and may include a plurality of consecutive subcarriers in one slot.

The number of OFDM symbols included in one slot may vary depending on the configuration of a cyclic prefix (CP). CP has an extended CP (normal CP) and a normal CP (normal CP). For example, when an OFDM symbol is configured by a general CP, the number of OFDM symbols included in one slot may be seven. When the OFDM symbol is configured by an extended CP, since the length of one OFDM symbol is increased, the number of OFDM symbols included in one slot is smaller than that of the normal CP. In the case of an extended CP, for example, the number of OFDM symbols included in one slot may be six. If the channel state is unstable, such as when the terminal moves at a high speed, an extended CP may be used to further reduce intersymbol interference.

When a general CP is used, since one slot includes 7 OFDM symbols, one subframe includes 14 OFDM symbols. In this case, the first two or three OFDM symbols of each subframe may be allocated to a physical downlink control channel (PDCCH), and the remaining OFDM symbols may be allocated to a physical downlink shared channel (PDSCH).

The structure of the radio frame is only an example, and the number of subframes included in the radio frame or the number of slots included in the subframe and the number of symbols included in the slot may be variously changed.

2 is an exemplary diagram illustrating an example of a resource grid for one downlink slot. This is the case in which an OFDM symbol consists of a normal CP. Referring to FIG. 2, the downlink slot includes a plurality of OFDM symbols in the time domain and includes a plurality of resource blocks in the frequency domain. Here, one downlink slot includes 7 OFDM symbols, and one resource block includes 12 subcarriers as an example, but is not limited thereto. Each element on the resource grid is called a resource element (RE). For example, the resource element a (k, l) becomes a resource element located in the k-th subcarrier and the l-th OFDM symbol. In the case of a normal CP, one resource block includes 12x7 resource elements (in the case of an extended CP, it includes 12x6 resource elements). Since the interval of each subcarrier is 15 kHz, one resource block includes about 180 kHz in the frequency domain. NDL is the number of resource blocks included in a downlink slot. The value of NDL may be determined according to a downlink transmission bandwidth set by scheduling of a base station.

3 is a diagram illustrating a structure of a downlink subframe. Up to three OFDM symbols at the front of the first slot in one subframe correspond to a control region to which a control channel is allocated. The remaining OFDM symbols correspond to data regions to which a physical downlink shared channel (PDSCH) is allocated. The basic unit of transmission is one subframe. That is, PDCCH and PDSCH are allocated over two slots. Downlink control channels used in the 3GPP LTE system include, for example, a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), and a Physical HARQ Indicator Channel. Physical Hybrid automatic repeat request Indicator Channel (PHICH). The PCFICH is transmitted in the first OFDM symbol of a subframe and includes information on the number of OFDM symbols used for control channel transmission in the subframe. The PHICH includes a HARQ ACK / NACK signal as a response of uplink transmission. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). DCI includes uplink or downlink scheduling information or an uplink transmit power control command for a certain terminal group. The PDCCH is a resource allocation and transmission format of the downlink shared channel (DL-SCH), resource allocation information of the uplink shared channel (UL-SCH), paging information of the paging channel (PCH), system information on the DL-SCH, on the PDSCH Resource allocation of upper layer control messages such as random access responses transmitted to the network, a set of transmit power control commands for individual terminals in an arbitrary terminal group, transmission power control information, and activation of voice over IP (VoIP) And the like. A plurality of PDCCHs may be transmitted in the control region. The terminal may monitor the plurality of PDCCHs. The PDCCH is transmitted in a combination of one or more consecutive Control Channel Elements (CCEs). CCE is a logical allocation unit used to provide a PDCCH at a coding rate based on the state of a radio channel. The CCE corresponds to a plurality of resource element groups. The format of the PDCCH and the number of available bits are determined according to the correlation between the number of CCEs and the coding rate provided by the CCEs. The base station determines the PDCCH format according to the DCI transmitted to the terminal, and adds a cyclic redundancy check (CRC) to the control information. The CRC is masked with an identifier called a Radio Network Temporary Identifier (RNTI) according to the owner or purpose of the PDCCH. If the PDCCH is for a specific terminal, the cell-RNTI (C-RNTI) identifier of the terminal may be masked to the CRC. Or, if the PDCCH is for a paging message, a paging indicator identifier (P-RNTI) may be masked to the CRC. If the PDCCH is for system information (more specifically, system information block (SIB)), the system information identifier and system information RNTI (SI-RNTI) may be masked to the CRC. Random Access-RNTI (RA-RNTI) may be masked to the CRC to indicate a random access response that is a response to the transmission of the random access preamble of the terminal.

4 is a diagram illustrating a structure of an uplink subframe. The uplink subframe may be divided into a control region and a data region in the frequency domain. A physical uplink control channel (PUCCH) including uplink control information is allocated to the control region. In the data area, a physical uplink shared channel (PUSCH) including user data is allocated. In order to maintain a single carrier characteristic, one UE does not simultaneously transmit a PUCCH and a PUSCH. PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers for two slots. This is called a resource block pair allocated to the PUCCH is frequency-hopped at the slot boundary.

Modeling of Multiple Antenna (MIMO) Systems

Multiple Input Multiple Output (MIMO) is a system that improves the transmission and reception efficiency of data by using multiple transmit antennas and multiple receive antennas.MIMO technology does not rely on a single antenna path to receive an entire message. The entire data may be received by combining a plurality of pieces of data received through.

MIMO technology includes a spatial diversity technique and a spatial multiplexing technique. The spatial diversity scheme can increase transmission reliability or widen a cell radius through diversity gain, which is suitable for data transmission for a mobile terminal moving at high speed. Spatial multiplexing can increase the data rate without increasing the bandwidth of the system by simultaneously transmitting different data.

5 is a configuration diagram of a wireless communication system having multiple antennas. As shown in FIG. 5 (a), when the number of transmit antennas is increased to NT and the number of receive antennas is increased to NR, theoretical channel transmission is proportional to the number of antennas, unlike a case where only a plurality of antennas are used in a transmitter or a receiver. Dose is increased. Therefore, the transmission rate can be improved and the frequency efficiency can be significantly improved. As the channel transmission capacity is increased, the transmission rate may theoretically increase as the rate of increase rate Ri multiplied by the maximum transmission rate Ro when using a single antenna.

For example, in a MIMO communication system using four transmit antennas and four receive antennas, a transmission rate four times higher than a single antenna system may be theoretically obtained. Since the theoretical capacity increase of multi-antenna systems was proved in the mid 90's, various techniques to actively lead to the actual data rate improvement have been actively studied. In addition, some technologies are already being reflected in various wireless communication standards such as 3G mobile communication and next generation WLAN.

The research trends related to multi-antennas to date include the study of information theory aspects related to the calculation of multi-antenna communication capacity in various channel environments and multi-access environments, the study of wireless channel measurement and model derivation of multi-antenna systems, improvement of transmission reliability, and improvement of transmission rate. Research is being actively conducted from various viewpoints, such as research on space-time signal processing technology.

The communication method in a multi-antenna system will be described in more detail using mathematical modeling. It is assumed that there are NT transmit antennas and NR receive antennas in the system.

Looking at the transmission signal, when there are NT transmit antennas, the maximum information that can be transmitted is NT. Each transmission information may have a different transmission power.

On the other hand, the transmission signal x may be considered in different ways according to two cases (for example, spatial diversity and spatial multiplexing). In the case of spatial multiplexing, different signals are multiplexed and the multiplexed signal is sent to the receiving side so that the elements of the information vector (s) have different values. On the other hand, in the case of spatial diversity, the same signal is repeatedly transmitted through a plurality of channel paths so that the elements of the information vector (s) have the same value. Of course, a combination of spatial multiplexing and spatial diversity techniques can also be considered. That is, the same signal may be transmitted through, for example, three transmit antennas according to a spatial diversity scheme, and the remaining signals may be spatially multiplexed and transmitted to the receiver.

In the case of modeling a channel in a multi-antenna wireless communication system, channels may be divided according to transmit / receive antenna indexes. A channel passing from the transmitting antenna j to the receiving antenna i will be denoted as hij. Note that in hij, the order of the index is the receive antenna index first, and the index of the transmit antenna is later.

5 (b) shows a channel from NT transmit antennas to receive antenna i. The channels may be bundled and displayed in vector and matrix form.

The real channel is added with white noise (AWGN) after going through the channel matrix.

The rank of a matrix is defined as the minimum number of rows or columns that are independent of each other. Thus, the rank of the matrix cannot be greater than the number of rows or columns.

In MIMO transmission, 'rank' indicates the number of paths that can independently transmit a signal, and 'number of layers' indicates the number of signal streams transmitted through each path. In general, since the transmitting end transmits the number of layers corresponding to the number of ranks used for signal transmission, unless otherwise specified, the rank has the same meaning as the number of layers.

Reference Signal; RS )

When transmitting a packet in a wireless communication system, since the transmitted packet is transmitted through a wireless channel, signal distortion may occur during the transmission process. In order to correctly receive the distorted signal at the receiving end, the distortion must be corrected in the received signal using the channel information. In order to find out the channel information, a method of transmitting the signal known to both the transmitting side and the receiving side and finding the channel information with the distortion degree when the signal is received through the channel is mainly used. The signal is called a pilot signal or a reference signal.

When transmitting and receiving data using multiple antennas, it is necessary to know the channel condition between each transmitting antenna and the receiving antenna to receive the correct signal. Therefore, a separate reference signal must exist for each transmit antenna.

In a mobile communication system, RSs can be classified into two types according to their purpose. One is an RS used for channel information acquisition, and the other is an RS used for data demodulation. Since the former is an RS for allowing the terminal to acquire downlink channel information, the former should be transmitted over a wide band, and even if the terminal does not receive downlink data in a specific subframe, it should be able to receive and measure the corresponding RS. Such RS is also used for measurement for handover and the like. The latter is an RS that is transmitted together with the corresponding resource when the base station transmits a downlink, and the terminal can estimate the channel by receiving the corresponding RS, thus demodulating data. This RS should be transmitted in the area where data is transmitted.

In the existing 3GPP LTE (eg, 3GPP LTE Release-8) system, two types of downlink RSs are defined for unicast services. One of them is a common RS (CRS) and the other is a dedicated RS (DRS). The CRS is used for measurement of channel state information, measurement for handover, and the like, and may be referred to as cell-specific RS. DRS is used for data demodulation and may be referred to as UE-specific RS. In the existing 3GPP LTE system, DRS is used only for data demodulation, and CRS can be used for both purposes of channel information acquisition and data demodulation.

The CRS is a cell-specific RS and is transmitted every subframe for a wideband. The CRS may be transmitted for up to four antenna ports according to the number of transmit antennas of the base station. For example, if the number of transmitting antennas of the base station is two, CRSs for

antenna ports

0 and 1 are transmitted, and if four, CRSs for antenna ports 0 to 3 are transmitted.

FIG. 6 is a diagram illustrating patterns of CRSs and DRSs on one resource block (14 OFDM symbols in time x 12 subcarriers in frequency in case of a general CP) in a system in which a base station supports four transmit antennas. In FIG. 6, resource elements RE denoted by 'R0', 'R1', 'R2' and 'R3' indicate positions of CRSs for

antenna port indexes

0, 1, 2, and 3, respectively. Meanwhile, the resource element denoted as 'D' in FIG. 6 indicates the position of the DRS defined in the LTE system.

LTE-A system of the advanced evolution of the LTE system, can support up to eight transmit antennas in the downlink. Therefore, RS for up to eight transmit antennas should also be supported. Since the downlink RS in the LTE system is defined for up to four antenna ports only, if the base station has four or more up to eight downlink transmission antennas in the LTE-A system, RSs for these antenna ports must be additionally defined. do. As RS for up to eight transmit antenna ports, both RS for channel measurement and RS for data demodulation should be considered.

One of the important considerations in designing an LTE-A system is backward compatibility. Backward compatibility means that the existing LTE terminal supports to operate correctly in the LTE-A system. From the point of view of RS transmission, if RS is added for up to eight transmit antenna ports in the time-frequency domain where CRS defined in the LTE standard is transmitted every subframe over the entire band, the RS overhead becomes excessively large. do. Therefore, in designing RS for up to 8 antenna ports, consideration should be given to reducing RS overhead.

RS newly introduced in LTE-A system can be classified into two types. One of them is an RS for channel measurement for selecting a transmission rank, a modulation and coding scheme (MCS), a precoding matrix index (PMI), and the like. Channel State Information RS (CSI-RS), and the other is a demodulation-reference signal (DM RS) which is an RS for demodulating data transmitted through up to eight transmit antennas.

CSI-RS for channel measurement purposes is characterized in that the CRS in the existing LTE system is designed for channel measurement-oriented purposes, unlike the CRS used for data demodulation at the same time as the channel measurement, handover, etc. have. Of course, the CSI-RS may also be used for the purpose of measuring handover. Since the CSI-RS is transmitted only for the purpose of obtaining channel state information, unlike the CRS in the existing LTE system, the CSI-RS does not need to be transmitted every subframe. Thus, to reduce the overhead of the CSI-RS, the CSI-RS may be designed to be transmitted intermittently (eg, periodically) on the time axis.

If data is transmitted on a downlink subframe, a DM RS is transmitted to a terminal scheduled for data transmission. The DM RS dedicated to a specific terminal may be designed to be transmitted only in a resource region in which the terminal is scheduled, that is, in a time-frequency region in which data for the terminal is transmitted.

7 is a diagram illustrating an example of a DM RS pattern defined in an LTE-A system. In FIG. 7, a position of a resource element in which a DM RS is transmitted is transmitted on one resource block in which downlink data is transmitted (14 OFDM symbols in time x 12 subcarriers in frequency). The DM RS may be transmitted for four antenna ports (

antenna port indexes

7, 8, 9 and 10) which are additionally defined in the LTE-A system. DM RSs for different antenna ports may be divided into being located in different frequency resources (subcarriers) and / or different time resources (OFDM symbols) (ie, may be multiplexed in FDM and / or TDM schemes). In addition, DM RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, multiplexed in the CDM manner). In the example of FIG. 7, DM RSs for

antenna ports

7 and 8 may be located in resource elements (REs) indicated as DM RS CDM group 1, which may be multiplexed by an orthogonal code. Likewise, DM RSs for

antenna ports

9 and 10 may be located in resource elements indicated as DM RS group 2 in the example of FIG. 7, which may be multiplexed by an orthogonal code.

8 is a diagram illustrating examples of a CSI-RS pattern defined in an LTE-A system. FIG. 8 shows the location of a resource element in which a CSI-RS is transmitted on one resource block in which downlink data is transmitted (14 OFDM symbols in time x 12 subcarriers in frequency). In any downlink subframe, one of the CSI-RS patterns of FIGS. 8 (a) to 8 (e) may be used. The CSI-RS may be transmitted for eight antenna ports (

antenna port indexes

15, 16, 17, 18, 19, 20, 21, and 22) which are additionally defined in the LTE-A system. CSI-RSs for different antenna ports may be divided into being located in different frequency resources (subcarriers) and / or different time resources (OFDM symbols) (ie, may be multiplexed in FDM and / or TDM schemes). In addition, CSI-RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, multiplexed in a CDM manner). In the example of FIG. 8 (a), CSI-RSs for

antenna ports

15 and 16 may be located in resource elements (REs) indicated as CSI-RS CDM group 1, which may be multiplexed by an orthogonal code. In the example of FIG. 8A, CSI-RSs for

antenna ports

17 and 18 may be located in resource elements indicated as CSI-RS CDM group 2, which may be multiplexed by an orthogonal code. In the example of FIG. 8 (a), CSI-RSs for antenna ports 19 and 20 may be located in resource elements indicated as CSI-RS CDM group 3, which may be multiplexed by an orthogonal code. In the example of FIG. 8A, CSI-RSs for

antenna ports

21 and 22 may be located in resource elements indicated as CSI-RS CDM group 4, which may be multiplexed by an orthogonal code. The same principle described with reference to FIG. 8 (a) may be applied to FIGS. 8 (b) to 8 (e).

The RS patterns of FIGS. 6 to 8 are merely exemplary and are not limited to specific RS patterns in applying various embodiments of the present invention. That is, even when RS patterns different from those of FIGS. 6 to 8 are defined and used, various embodiments of the present invention may be equally applied.

CSI- RS Configuration

One CSI process is defined by associating one CSI-RS resource for signal measurement and one Interference Measurement resource (IMR) for interference measurement among a plurality of CSI-RSs and a plurality of IMRs configured for the UE. Can be. The UE feeds back CSI information derived from different CSI processes to a network (eg, a base station) with independent periods and subframe offsets.

That is, each CSI process has an independent CSI feedback setting. The CSI-RS resource, IMR resource association information, and CSI feedback configuration may be informed by the base station to the UE through higher layer signaling such as RRC for each CSI process. For example, it is assumed that the UE receives (sets) three CSI processes as shown in Table 1 below.

Table 1

In Table 1, CSI-RS 0 and CSI-RS 1 indicate CSI-RSs received from Cell 2, which is a neighboring cell participating in cooperation with CSI-RS, which is received from Cell 1, which is a serving cell of a UE. If it is assumed that the IMR set for each CSI process of Table 1 is set as shown in Table 2,

TABLE 2

In IMR 0, cell 1 performs muting, cell 2 performs data transmission, and the UE is configured to measure interference from cells other than cell 1 from IMR 0. Similarly, in IMR 1, cell 2 muting, cell 1 performs data transmission, and the UE is configured to measure interference from cells other than cell 2 from IMR 1. In addition, in IMR 2, both cell 1 and cell 2 perform muting, and the terminal is configured to measure interference from cells other than cell 1 and cell 2 from IMR 2.

Therefore, as shown in Table 1 and Table 2, CSI information of CSI process 0 represents optimal RI, PMI, CQI information when receiving data from cell 1. CSI information of CSI process 1 represents optimal RI, PMI, and CQI information when data is received from cell 2. CSI information of CSI process 2 represents optimal RI, PMI, and CQI information when data is received from cell 1 and no interference is received from cell 2.

It is preferable that a plurality of CSI processes configured (configured) for one UE share a mutually dependent value. For example, in the case of joint transmission (JT) of Cell 1 and Cell 2, the channel of CSI Process 1 and Cell 2, which regards the channel of Cell 1 as a signal part, is regarded as the signal part. When the CSI process 2 is configured (configured) to one UE, the ranks of the CSI process 1 and the CSI process 2 and the selected subband index are the same to facilitate JT scheduling.

The period or pattern in which the CSI-RS is transmitted may be configured by the base station. In order to measure the CSI-RS, the UE must know the CSI-RS configuration for each CSI-RS antenna port of the cell to which the UE belongs. The CSI-RS configuration includes a downlink subframe index in which the CSI-RS is transmitted and a time-frequency position of the CSI-RS resource element (RE) in the transmission subframe (for example, FIGS. 8A to 8E). CSI-RS pattern), and CSI-RS sequence (a sequence used for CSI-RS purposes), which are pseudo-random according to a predetermined rule based on a slot number, a cell ID, a CP length, and the like. Generated), and the like. That is, a plurality of CSI-RS configurations may be used in any base station, and the base station may inform the CSI-RS configuration to be used for the terminal (s) in the cell among the plurality of CSI-RS configurations.

In addition, since the CSI-RS for each antenna port needs to be distinguished, resources to which the CSI-RS is transmitted for each antenna port should be orthogonal to each other. As described in connection with FIG. 8, CSI-RSs for each antenna port may be multiplexed in an FDM, TDM and / or CDM scheme using orthogonal frequency resources, orthogonal time resources, and / or orthogonal code resources. have.

When the base station informs the UEs in the cell of the CSI-RS information (CSI-RS configuration), it is necessary to first inform the information about the time-frequency to which the CSI-RS for each antenna port is mapped. Specifically, the time information includes subframe numbers through which CSI-RSs are transmitted, periods through which CSI-RSs are transmitted, subframe offsets through which CSI-RSs are transmitted, and CSI-RS resource elements (RE) of a specific antenna. OFDM symbol numbers to be transmitted may be included. The information about the frequency may include a frequency spacing through which the CSI-RS resource element RE of a specific antenna is transmitted, an offset or shift value of the RE on the frequency axis, and the like.

9 is a diagram for explaining an example of a method in which a CSI-RS is periodically transmitted. The CSI-RS may be periodically transmitted with an integer multiple of one subframe (eg, 5 subframe periods, 10 subframe periods, 20 subframe periods, 40 subframe periods, or 80 subframe periods). .

In FIG. 9, one radio frame includes 10 subframes (subframe numbers 0 to 9). In FIG. 9, for example, the transmission period of the CSI-RS of the base station is 10 ms (ie, 10 subframes), and the CSI-RS transmission offset is 3. The offset value may have a different value for each base station so that CSI-RS of several cells may be evenly distributed in time. When the CSI-RS is transmitted in a period of 10 ms, the offset value may have one of 0 to 9. Similarly, for example, when the CSI-RS is transmitted with a period of 5 ms, the offset value may have one of 0 to 4, and when the CSI-RS is transmitted with a period of 20 ms, the offset value is one of 0 to 19. When CSI-RS is transmitted in a period of 40 ms, the offset value may have one of 0 to 39. When CSI-RS is transmitted in a period of 80 ms, the offset value is one of 0 to 79. It can have a value of. This offset value indicates the value of the subframe where the base station transmitting the CSI-RS at a predetermined period starts the CSI-RS transmission. When the base station informs the transmission period and the offset value of the CSI-RS, the terminal may receive the CSI-RS of the base station at the corresponding subframe location by using the value. The terminal may measure the channel through the received CSI-RS and report information such as CQI, PMI and / or Rank Indicator (RI) to the base station as a result. Except where CQI, PMI, and RI are distinguished from each other in this document, these may be collectively referred to as CQI (or CSI). In addition, the CSI-RS transmission period and offset may be separately designated for each CSI-RS configuration.

10 is a diagram for explaining an example of a method in which a CSI-RS is transmitted aperiodically. In FIG. 10, one radio frame includes 10 subframes (subframe numbers 0 to 9). As shown in FIG. 10, the subframe in which the CSI-RS is transmitted may appear in a specific pattern. For example, the CSI-RS transmission pattern may be configured in units of 10 subframes, and whether or not to transmit CSI-RS in each subframe may be designated as a 1-bit indicator. 10 illustrates a CSI-RS pattern transmitted at

subframe indexes

3 and 4 within 10 subframes (subframe indexes 0 to 9). Such an indicator may be provided to the terminal through higher layer signaling.

Configuration of the CSI-RS transmission may be configured in various ways as described above, and in order for the terminal to correctly receive the CSI-RS and perform channel measurement, the base station needs to inform the terminal of the CSI-RS configuration. There is. Embodiments of the present invention for informing the UE of the CSI-RS configuration will be described below.

CSI- RS How to tell your settings

In general, the following two methods may be considered as a method of informing the UE of the CSI-RS configuration.

The first method is a method in which a base station broadcasts information on a CSI-RS configuration to terminals by using a dynamic broadcast channel (DBCH) signaling.

In a conventional LTE system, when a base station notifies UEs about system information, the information may be transmitted through a BCH (broadcasting channel). If there is a lot of information about the system information to inform the terminal, the base station transmits the system information in the same manner as the general downlink data, but only the BCH, the PDCCH CRC of the corresponding data to a specific terminal identifier (for example, System information may be transmitted by masking using a system information identifier (SI-RNTI) rather than a C-RNTI. In this case, the actual system information is transmitted on the PDSCH region like general unicast data. Accordingly, all terminals in the cell can obtain system information by decoding the PDCCH using the SI-RNTI and then decoding the PDSCH indicated by the corresponding PDCCH. Such a broadcasting method may be referred to as a dynamic BCH (DBCH) by distinguishing it from a physical broadcasting (PBCH) which is a general broadcasting method.

On the other hand, system information broadcast in the existing LTE system can be largely divided into two. One of them is a master information block (MIB) transmitted through a PBCH, and the other is a system information block (SIB) transmitted by being multiplexed with general unicast data on a PDSCH region. Since information transmitted as SIB type 1 to SIB type 8 (SIB1 to SIB8) is defined in an existing LTE system, information about CSI-RS configuration, which is new system information not defined in the existing SIB type, is defined. You can define a new SIB type. For example, the SIB9 or SIB10 may be defined, and the base station may inform the UEs in the cell of the CSI-RS configuration through the DBCH scheme.

The second method is a method in which a base station informs each terminal of information about a CSI-RS configuration using Radio Resource Control (RRC) signaling. That is, information on the CSI-RS configuration may be provided to each of the terminals in the cell by using dedicated RRC signaling. For example, in a process of establishing a connection with a base station through an initial access or handover, the base station may inform the terminal of the CSI-RS configuration through RRC signaling. . Alternatively, when the base station transmits an RRC signaling message for requesting channel state feedback based on the CSI-RS measurement, the base station may inform the terminal of the CSI-RS configuration through the corresponding RRC signaling message.

CSI- RS Indication of the setting

A plurality of CSI-RS configurations may be used in any base station, and the base station may transmit CSI-RSs according to each CSI-RS configuration to the UE on a predetermined subframe. In this case, the base station informs the user equipment of a plurality of CSI-RS configurations, and among them, what is the CSI-RS to be used for channel state measurement for channel quality information (CQI) or channel state information (CSI) feedback? You can let them know.

As described above, an embodiment of the CSI-RS configuration to be used in the terminal and the indication of the CSI-RS to be used for channel measurement will be described below.

FIG. 11 is a diagram for explaining an example in which two CSI-RS configurations are used. In FIG. 11, one radio frame includes 10 subframes (subframe numbers 0 to 9). In FIG. 11, the first CSI-RS configuration, that is, the CSI-RS1 has a CSI-RS transmission period of 10 ms and a CSI-RS transmission offset of 3. In FIG. 11, the second CSI-RS configuration, that is, the CSI-RS2 has a CSI-RS transmission period of 10 ms and a CSI-RS transmission offset of 4. The base station informs the user equipment of two CSI-RS configurations, and can inform which CSI-RS configuration is used for CQI (or CSI) feedback.

When the terminal receives a request for CQI feedback for a specific CSI-RS configuration from the base station, the terminal may perform channel state measurement using only the CSI-RS belonging to the corresponding CSI-RS configuration. Specifically, the channel state is determined as a function of the CSI-RS reception quality and the amount of noise / interference and the correlation coefficient. The CSI-RS reception quality measurement is performed using only the CSI-RS belonging to the corresponding CSI-RS configuration. In order to measure the amount of noise / interference and the correlation coefficient (e.g., an interference covariance matrix indicating the direction of the interference), the measurement may be performed in the corresponding CSI-RS transmission subframe or in designated subframes. Can be. For example, in the embodiment of FIG. 11, when the UE receives a request for feedback from the base station from the first CSI-RS configuration (CSI-RS1), the UE receives a fourth subframe (subframe index 3 of one radio frame). RSI is performed using CSI-RS transmitted from the Rx), and it may be designated to use an odd-numbered subframe separately for measuring the amount of noise / interference and correlation coefficient. Alternatively, the CSI-RS reception quality measurement and the amount of noise / interference and the correlation coefficient measurement may be specified to be limited to a specific single subframe (for example, subframe index 3).

For example, the received signal quality measured using CSI-RS is signal-to-interference plus noise ratio (SINR), which is simply S / (I + N) where S is received. Strength of the signal, I is the amount of interference, N is the amount of noise). S may be measured through the CSI-RS in the subframe including the CSI-RS in the subframe including the signal transmitted to the UE. Since I and N change according to the amount of interference from the neighboring cell, the direction of the signal from the neighboring cell, and the like, it can be measured through a CRS transmitted in a subframe for measuring S or a subframe separately designated.

The measurement of the amount of noise / interference and the correlation coefficient may be performed at a resource element (RE) to which a CRS or CSI-RS is transmitted in a corresponding subframe, or is set to facilitate measurement of noise / interference. It can also be done through a null resource element (Null RE). In order to measure noise / interference in the CRS or CSI-RS RE, the UE first recovers the CRS or CSI-RS, and then subtracts the result from the received signal to leave only the noise and interference signals. Statistics of noise / interference can be obtained. A null RE means a RE that the base station is empty without transmitting any signal (that is, the transmission power is zero (zero)) and facilitates signal measurement from other base stations except the base station. CRS RE, CSI-RS RE, and Null RE may all be used to measure the amount of noise / interference and the correlation coefficient, but the base station may designate to the terminal as to which of these REs to measure the noise / interference. have. This is because it is necessary to appropriately designate the RE to be measured by the corresponding UE according to whether the signal of the neighbor cell transmitted to the RE location where the UE performs measurement is a data signal or a control signal, and the neighbor cell transmitted at the corresponding RE location. What is the signal of depends on whether the synchronization between the cells and the CRS configuration (configuration) and CSI-RS configuration (configuration), so that the base station can determine this to determine the measurement to perform the UE. That is, the base station may designate the terminal to measure noise / interference by using all or part of CRS RE, CSI-RS RE, and Null RE.

For example, the base station may use a plurality of CSI-RS configuration, the base station informs the terminal of one or more CSI-RS configuration, and among them, the CSI-RS configuration to be used for CQI feedback And Null RE location. The CSI-RS configuration to be used for CQI feedback by the terminal is expressed in terms of distinguishing it from a Null RE transmitted with a transmission power of 0, and a CSI-RS configuration transmitted with a non-zero transmission power. configuration). For example, the base station informs one CSI-RS configuration in which the terminal will perform channel measurement, and the terminal indicates that the CSI-RS is non-zero in the one CSI-RS configuration. It can be assumed to be transmitted at the transmit power. In addition, the base station informs about the CSI-RS configuration (that is, about the Null RE location) transmitted at a transmission power of 0, and the terminal is located at the resource element (RE) location of the corresponding CSI-RS configuration. It can be assumed that the transmission power of 0 for (assume). In other words, the base station informs the user equipment of one CSI-RS configuration of non-zero transmission power, and if there is a CSI-RS configuration of transmission power of 0, the terminal indicates the corresponding Null RE location. You can let them know.

As a variation of the above CSI-RS configuration indicating method, the base station informs a plurality of CSI-RS configuration to the terminal, among which all or part of the CSI-RS configuration to be used for CQI feedback ( configuration). Accordingly, the UE, which has received CQI feedback for a plurality of CSI-RS configurations, measures CQIs using CSI-RSs corresponding to each CSI-RS configuration, and measures the measured CQIs. Information can be sent together to the base station.

Alternatively, the base station may designate uplink resources required for transmitting the CQI of the terminal in advance for each CSI-RS configuration so that the terminal may transmit CQI for each of a plurality of CSI-RS configurations. The information on the uplink resource designation may be provided to the terminal in advance through RRC signaling.

Alternatively, the base station may dynamically trigger the terminal to transmit CQI for each of a plurality of CSI-RS configurations to the base station. Dynamic triggering of CQI transmission may be performed over the PDCCH. Which CSI-RS configuration (CQI measurement) to be performed may be known to the UE through the PDCCH. The terminal receiving the PDCCH may feed back the CQI measurement result for the CSI-RS configuration designated in the corresponding PDCCH to the base station.

The transmission time of the CSI-RS corresponding to each of the plurality of CSI-RS configurations may be designated to be transmitted in another subframe or may be designated to be transmitted in the same subframe. When transmission of CSI-RSs according to different CSI-RS configurations is designated in the same subframe, it is necessary to distinguish them from each other. In order to distinguish CSI-RSs according to different CSI-RS configurations, one or more of time resources, frequency resources, and code resources of CSI-RS transmission may be differently applied. For example, the transmission RE position of the CSI-RS in the corresponding subframe is different according to the CSI-RS configuration (for example, the CSI-RS according to one CSI-RS configuration is the RE position of FIG. 8 (a)). CSI-RS transmitted from the CSI-RS according to another CSI-RS configuration may be designated to be transmitted in the RE position of FIG. 8 (b) in the same subframe (division using time and frequency resources). Alternatively, when CSI-RSs according to different CSI-RS configurations are transmitted in the same RE location, the CSI-RS scrambling codes may be differently used in different CSI-RS configurations to distinguish them from each other. It may be possible (division using code resources).

AAS (Active Antenna System)AAS (Active Antenna System)

After LTE Release-12, an antenna system utilizing AAS will be introduced. AAS (Active Antenna System) is composed of an active antenna each antenna includes an active circuit. AAS is expected to reduce the interference by changing the antenna pattern according to the situation, or to perform beamforming more efficiently. When the AAS is constructed in two dimensions (2D-AAS), the main lobe of the antenna can be more efficiently adjusted in three dimensions in terms of the antenna pattern, and the transmission beam can be changed more actively according to the position of the receiver.

12 shows an example of a 64 port 2D-AAS antenna arrangement.

Referring to FIG. 12, the 2D-AAS may install an antenna in a vertical direction and a horizontal direction to construct a large amount of antenna system.

When 2D-AAS is introduced, the transmitting end should send a specific RS (eg, CSI-RS, hereinafter referred to as “CSI-RS” for convenience) to inform the receiving end of the channel from the transmitting end to the receiving end. In the current LTE system, CSI-RS is designed as 1 port, 2 ports, 4 ports, 8 ports CSI-RS. Each n-ports CSI-RS with n> 1 must use n REs for one RB. Therefore, in the case of 2D-AAS, if there are 8 antennas in the vertical direction and 8 in the horizontal direction, and thus have 64 antennas in total, 64 REs are used in one RB for the CSI-RS. do. Therefore, CSI-RS overhead depending on the number of antennas may be a problem.

To solve this problem, it is possible to use only a few CSI-RS ports to infer the channel coming from the remaining ports. As one method for this, the channel from the 2D-AAS to the receiver can be estimated as the kronecker product as follows.

[Equation 1]

In Equation 1, H means an entire channel from a transmitting end to a receiving end, and H _T ^(j) means a channel from a transmitting end to a jth receiving antenna. H _v ^(j) and H _H ^(j) mean channels transmitted from the antenna element (or port) in the vertical direction and the horizontal direction to the jth antenna of the receiver, respectively. In FIG. 12, it is assumed that only the antenna of the A block exists, and H _V ^(j) means a channel for the j-th antenna of the receiver from the A block antenna. H _H ^(j) assumes that only the antenna of the B block exists, and means a channel for the j-th antenna of the receiver from the antenna of the B block.

Hereinafter, for the convenience of explanation, the description will be made from any one reception antenna position, and all processes may be applied to all other reception antennas. In addition, the following description will be made using only channels up to any one receiving antenna from which the (j) index is removed at the transmitting end.

[Equation 2]

On the other hand, Equation 2 is an equation for explaining the present invention, the present invention can be applied even if the actual channel is not the same as the equation (2).

Two CSI-RSs may be configured by setting one CSI-RS having the antenna port Nv in the vertical direction as shown in A block of FIG. 12 and one CSI-RS having the antenna port N _H in the horizontal direction as shown in the B block. . After receiving two CSI-RSs, the receiver can infer a channel by Kronecker product of two channel matrices as shown in Equation 2. Nv is the number of antennas in the vertical direction, and N _H is the number of antennas in the horizontal direction. Using this method, even if the existing 2, 4, 8 port CSI-RS, even the channel coming from 64 port can be informed to the receiver.

Instead of the co-polarized antenna array shown in FIG. 12, a cross-polarized antenna array (hereinafter referred to as X-pol AA) as shown in FIG. 13 may be considered. In this case, the 64 ports antenna array can be configured as 8 row / 4 column x 2 polarization as shown in FIG.

14 is an illustration of an A / B block in X-pol AA.

In summary, in an N-tx Massive MIMO environment where a base station has a large number of transmit antennas, N-Tx CSI-RS and N-Tx PMI must be newly defined for CSI feedback, but RS overhead or feedback overhead is considered. In this case, it may be difficult to newly define N-Tx CSI-RS and PMI. As an alternative, the conventional M-Tx (M = 8 or less) antenna CSI-RS and M-Tx PMI may be used to support massive MIMO feedback. In more detail, it can operate as one of two feedback methods.

As a first feedback method, a part of the massive antenna may be set to CSI-RS in each of multiple CSI processes, and the UE may feed back CSI for each process. For example, CSI processes 1 and 2 are set to one UE, process 1 configures CSI-RS 1 corresponding to block A of FIG. 14 and process 2 configures CSI-RS 2 corresponding to block B of FIG. 14. give. The UE raises feedback on the CSI-

RSs

1 and 2 by using the CSI feedback chain configured for the two processes.

However, the following problem exists in this case.

As a first problem, the CQI of each CSI process indicates the MCS that can be obtained when only a few of the massive antennas are used, not the CQIs that can be achieved when the entire massive antennas are used. In this case, the base station receives the CQI of each CSI process and it is difficult to recalculate the CQI that can be achieved when using the entire massive antenna.

As a second problem, the RI of each CSI process indicates the RI that can be obtained when only a few of the massive antennas are used, not the RIs that can be achieved when the entire massive antennas are used. In this case, even if the base station receives the RI of each CSI process and recalculates the RI that can be achieved when using the entire massive antenna, it is difficult to recalculate the CQI corresponding to the recalculated RI.

As a third problem, the PMI of the CSI process indicates the PMI that can be obtained when only a few of the massive antennas are used, rather than the optimal PMI when the entire massive antennas are used.

To solve this problem, we can consider the following second feedback method.

As a second Massive MIMO feedback method to solve the problem of the first feedback method, a CSI process is configured for the UE, and the UE feeds back RI, PMI, and CQI that can be achieved when using the entire Massive Antenna through the process. There is a way. At this time, L CSI-RSs corresponding to one IMR and a massive MIMO antenna may be configured in one CSI process. That is, CSI process related information may be configured as follows.

CSI process information = {IMR setting, 1st CSI-RS setting, 2nd CSI-RS setting,… , L-th CSI-RS Settings}

In this way, the UE can estimate the total Massive MIMO channel from L CSI-RSs, and feeds back the entire channel into K PMIs.In consideration of the PUCCH feedback format, all K are due to the limitation of payload size. There is a problem that can not feed back the PMI at once. That is, there is a big overhead in feeding back multiple PMIs corresponding to each of multiple CSI-RSs at once.

Therefore, the following embodiments of the present invention can be applied to solve this problem.

본 발명에 따른 실시예Embodiment according to the present invention

The present invention relates to a method for feeding back a CSI with which CSI is information on which partial channel of the entire channel with the base station. In a massive MIMO environment having a large number of transmit antennas, a base station can inform a UE of some or all channels of the transmit antenna through several CSI-RS configurations. At this time, the UE ideally quantizes all channel information with the base station to PMI and feeds back at once, but considering realistic feedback overhead, after dividing the entire channel into several partial channels, the corresponding PMI is sequentially fed back. Can be. According to the present invention, the UE updates and updates only the PMI having the most effect, and informs the base station about which partial channel the PMI is determined based on, thereby reducing feedback overhead.

In more detail, the UE may select one of the K partial channels and feed back only the PMI corresponding to the selected partial channel. In this case, the CSI feedback capable partial channel candidate should be promised between the base station and the UE, and a separate control signal may be set for this purpose. When partial channels A and B each have a one-to-one correspondence with different CSI-RSs, partial channel selection for CSI feedback has the same meaning as selection of CSI-RS.

For example, the base station informs the UE of the CSI-RS corresponding to the A block of FIG. 14 and the CSI-RS corresponding to the B block, and the UE transmits a downlink channel for vertical antennas through the CSI-RS corresponding to the A block. The PMI is calculated by estimating the PMI, and the PMI is calculated by estimating the downlink channels of the horizontal antennas through the CSI-RS corresponding to the B block. When the former is referred to as vertical PMI and the latter as horizontal PMI, the partial channels A and B selected by the UE can mean vertical PMI and horizontal PMI, respectively. Alternatively, partial channels A and B may not have a one-to-one correspondence with the CSI-RS. For example, partial channel A may mean a composite channel of a channel estimated from two CSI-RSs, and partial channel B may mean a channel estimated from one CSI-RS.

Hereinafter, a method of selecting partial channel information by the UE and a specific method of feeding back CSI of the selected partial channel to the base station will be described.

제1 실시예(부분 채널 선택 방법)First Embodiment (Partial Channel Selection Method)

A first embodiment according to the present invention is directed to a method for a UE to select a partial channel.

In detail, the UE may select the partial channel with the most severe channel change and provide PMI feedback. This is because in the case of the partial channel where the channel change is not severe, the PMI sent in the past may be valid to some extent, so that it is effective to feed back the PMI of the partial channel with the severe channel change.

Alternatively, the UE may select the partial channel so that the CQI that can be obtained when updating the PMI is maximized. The UE calculates the CQI for each case by considering all selectable partial channels, and selects the partial channel having the largest CQI among them.

제2 실시예(선택된 부분 채널을 피드백하는 방법)Second embodiment (method of feeding back the selected partial channel)

A second embodiment according to the present invention is directed to a method in which a UE feeds back a selected partial channel to a base station.

The UE selects one partial channel among all partial channel candidates and calculates and feeds back a PMI based on the partial channel candidate. At this time, the base station must know which partial channel the PMI fed back by the UE corresponds to. The simplest way to feed back this information is to feed back information about the selected partial channel with the PMI.

For example, when there are two partial channels corresponding to blocks A and B, as shown in FIG. 14, the UE selects one of two partial channels whenever PMI feedback is provided and calculates the PMI based on the partial channel. And feed back the selected partial channel candidate.

15 is an example of a feedback setting according to an embodiment of the present invention.

When the feedback mode is set as shown in FIG. 15, a partial channel is additionally selected (for example, PCI: partial CSI indicator) in addition to all subframes to which W1 and W2 are fed back. In this case, since two partial channels are assumed, PCI is expressed as 1 bit, and when PCI is 0 and 1, it means partial channels corresponding to 1st column vertical antennas and 1st row horizontal antennas, respectively.

By default, independent PCI is fed back in every subframe where W1 and W2 are fed back, but you can also use PCI to feed back only with either W1 or W2. For example, PCI is fed back only with W1, and the CSI-RS of W2 is determined by the most recently reported PCI value. Meanwhile, in FIG. 15, W1 and W2 represent respective codebooks in the dual codebook, such as LTE 8Tx codebook or enhanced 4Tx codebook, RI means rank, and CQI means channel quality indicator.

Each partial channel may have a different codebook structure (eg, dual codebook or single codebook). For example, the A block of FIG. 14 uses a single codebook structure suitable for the ULA structure and the B block uses a dual codebook structure suitable for the X-Pol structure. To this end, the base station may signal a codebook to be used for feedback for each partial channel to the UE. In this case, the CSI feedback frame is set according to a more complex dual codebook, and when a single codebook PMI is fed back, the UE feeds back a single PMI instead of W1 or W2. Hereinafter, more specific embodiments will be described.

If the codebook corresponding to the partial channel 1 in FIG. 15 has a dual structure consisting of W1 and W2, but the codebook corresponding to the partial channel 2 has a single structure (for example, a release-8 LTE 4Tx codebook), the reporting structure of FIG. Feedback of the codebook of partial channel 2 is ambiguous. In this case, W1 jointly encoded with RI is assumed to be a codebook corresponding to partial channel 1, and feedback is performed without PCI, and PCI is fed back together only when W2 is fed back. As a result, it may be indicated whether W2 shown in FIG. 15 is W2 of partial channel 1 or single PMI of partial channel 2. FIG.

Alternatively, in order to prevent the complexity of the codebook structure as described above, the UE may limit the CSI feedback to be performed using the same codebook structure for all partial channels.

In FIG. 15, the CQI is fed back with the updated PMI. At this time, the CQI is a value that can be achieved when the base station performs massive MIMO using the most recent PMIs, including the time point at which the CQI is fed back. The RI may be a value in which different ranks corresponding to each of the multiple CSI-RSs are jointly encoded, or a single value commonly applied to the PMIs of all the multiple CSI-RSs.

In addition, the embodiment of FIG. 15 is a method of feeding back PCI together at every PMI feedback moment. In this case, the frequency of feeding back PCI may be inefficient in terms of feedback overhead. For example, in FIG. 14, when the channel change rates of the partial channel 1 and the partial channel 2 corresponding to each of the vertical antenna and the horizontal antenna are asymmetric, inefficiency increases. In this case, PCI can be fed back over a longer period. For example, the UE feeds back PCI with the RI and reports the PMI corresponding to the same partial channel until the next PCI + RI is updated.

Alternatively, the PCI may be fed back with the RI, but may operate as follows. If PCI = 0, the PMI is fed back to the partial channel 1 for a certain time from the PCI report time, and the PMI is fed back to the partial channel 2 until the next PCI is reported. In this case, the predetermined time may be a RRC signaling or a fixed value to the UE in advance. If PCI = 1, feed back the PMI for partial channel 2 from the PCI report time until the next PCI is reported.

16 is an example of such a feedback method. If the channel speed of the vertical antenna is slower than the channel of the horizontal antenna, the

partial channels

1 and 2 may be mapped to the vertical antenna and the horizontal antenna, respectively, and set as shown in FIG. 16 to provide more effective feedback.

In FIG. 16, the PMI corresponding to the partial channel 1 has been transmitted at a later time for a certain period of time. However, when PCI = 0, the PMI corresponding to the partial channel 1 maintains a uniform ratio with the PMI corresponding to the partial channel 2 in another method. Can be fed back at one time interval. In FIG. 17, the PMI corresponding to the partial channel 1 and the PMI corresponding to the partial channel 2 are reported at equal intervals while maintaining a feedback ratio of 1: 2. This feedback rate can be informed by the base station to the UE.

Alternatively, the feedback ratio of the PMI corresponding to the partial channel 1 and the PMI corresponding to the partial channel 2 may be differently set according to the PCI value. FIG. 18 shows an example in which two PMIs are reported at equal intervals with a ratio of 1: 2 when PCI = 0, and two PMIs are reported at equal intervals with a ratio of 1: 1 when PCI = 1. This feedback rate can be informed by the base station to the UE.

Alternatively, the feedback ratio of the PMI corresponding to the partial channel 1 and the PMI corresponding to the partial channel 2 may be interchanged according to the PCI value. For example, it is possible to select a feedback ratio between the two PMIs through a signaling between the base station and the UE at 1: 2 and to select a feedback ratio of 1: 2 to the two PMIs according to PCI. FIG. 19 shows that PMI corresponding to partial channel 1 and PMI corresponding to partial channel 2 are reported at equal intervals with a ratio of 1: 2 when PCI = 0, and PMI corresponding to partial channel 2 when PCI = 1. For example, the PMI corresponding to the partial channel 1 is reported at equal intervals with a ratio of 1: 2.

When using the PCI value as shown in FIG. 19 (that is, when using the PCI for the purpose of changing the feedback ratio of the PMI corresponding to each partial channel), the existing mode 2-1 may be modified as shown in FIGS. 20 to 23. . 20 is an example of the case of PCI = 1 and PTI = 0, FIG. 21 is an example of the case of PCI = 0 and PTI = 1, and FIG.22 is an example of the case of PCI = 1 and PTI = 1.

Here, the PMI feedback ratio of the two partial channels is set to 1: 3, and Wi1 having a long-term / wideband property is fed back with a long period compared to Wi2, so it is transmitted along with the PMI of another partial channel transmitted over a long period. That is, in

subframes

1 and 9 of FIGS. 20 and 21, the PMI for one partial channel and the longterm / wideband PMI for the remaining partial channel are reported together.

20 to 23, if the codebook of the partial channel 1 is a single codebook, one of W1--1 or W1--2 is not assumed to be reported as an identity precoder, and the other one of W1--1 or W1--2 is signleed. You can report by replacing it with a codebook. The same rule applies to the case where the PMI subchannel 2 is a single codebook.

In the above-described embodiment, the PCI is applied only to the PMI feedback, but may be extended to the remaining CSI feedback (eg, RI or CQI).

For example, if PCI is applied to RI, the fed back RI means the rank of the channel of the partial channel indicated by PCI. In this case, the PCI in Figs. 16 to 18 tells which partial channel the RI value transmitted together is calculated from.

If the concept of PCI is applied to CQI, the feedback CQI means the CQI of the channel of the partial channel indicated by PCI. In this case, in FIG. 15, the PCI indicates which partial channel the CQI value transmitted together is calculated from the channel. In addition, CQI feedback may be applied in the same manner as the PMI feedback operation according to PCI in FIGS. 16 to 18.

24 is a flowchart showing an example of an embodiment of the present invention.

First, the UE receives CSI configuration information for CSI reporting (S2401). Next, identification information on the partial channel corresponding to the CSI among the entire channels according to the CSI and the massive MIMO is transmitted based on the CSI configuration information (S2403). Detailed contents thereof are the same as those of the first and second embodiments described above, and thus detailed description thereof will be omitted.

25 illustrates a base station and a terminal that can be applied to an embodiment of the present invention.

When a relay is included in the wireless communication system, communication is performed between the base station and the relay in the backhaul link, and communication is performed between the relay and the terminal in the access link. Therefore, the base station or the terminal illustrated in the figure may be replaced with a relay according to the situation.

Referring to FIG. 25, a wireless communication system includes a base station 2510 and a terminal 2520. The base station 2510 includes a processor 2513, a memory 2514, and radio frequency (RF)

units

2511, 2512. The processor 2513 may be configured to implement the procedures and / or methods proposed by the present invention. The memory 2514 is connected to the processor 2513 and stores various information related to the operation of the processor 2513. The RF unit 2516 is connected with the processor 2513 and transmits and / or receives a radio signal. The terminal 2520 includes a processor 2523, a memory 2524, and

RF units

2521 and 2522. The processor 2523 may be configured to implement the procedures and / or methods proposed by the present invention. The memory 2524 is connected to the processor 2523 and stores various information related to the operation of the processor 2523. The

RF units

2521 and 2522 are connected to the processor 2523 and transmit and / or receive a radio signal. The base station 2510 and / or the terminal 2520 may have a single antenna or multiple antennas.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

Certain operations described in this document as being performed by a base station may in some cases be performed by an upper node thereof. That is, it is obvious that various operations performed for communication with the terminal in a network including a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A base station may be replaced by terms such as a fixed station, a Node B, an eNodeB (eNB), an access point, and the like.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), and FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor.

The memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable those skilled in the art to implement and practice the invention. Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the present invention. For example, those skilled in the art can use each of the configurations described in the above-described embodiments in combination with each other. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The invention can be embodied in other specific forms without departing from the spirit and essential features of the invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship or may be incorporated as new claims by post-application correction.

The present invention can be used in a wireless communication device such as a terminal, a relay, a base station, and the like.

Claims

In a method for a terminal to transmit channel state information (CSI) in a wireless access system supporting massive MIMO (Massive) Multiple Input Multiple Output (MIMO),

Receiving CSI configuration information for CSI reporting; And

Transmitting identification information of a partial channel corresponding to the CSI among all channels according to the CSI and the massive MIMO based on the CSI configuration information;

The channel state information transmission method comprising a.
The method of claim 1,

When the identification information is the first value, the partial channel corresponds to the antenna of the first column of the antenna array according to the massive MIMO,

And when the identification information is the second value, the partial channel corresponds to the antenna of the first row of the antenna array according to the massive MIMO.
The method of claim 1,

The partial channel is associated with a single codebook when the identification information is a first value,

And the partial channel is associated with a dual codebook when the identification information is a second value.
The method of claim 1,

When the identification information is the first value, the partial channel indicates that the ratio of the feedback frequency of the first partial channel and the second partial channel has a first ratio value,

And when the identification information is the second value, the partial channel indicates that the ratio of the feedback frequency of the first partial channel and the second partial channel has a second ratio value.
The method of claim 1,

The identification information is transmitted together with the CSI only when the CSI is a wideband PMI (Precoding Matrix Indicator), and is not transmitted together when the CSI is a narrowband PMI.
The method of claim 1,

And the identification information is fed back with a Rank Indicator (RI), and a Precoding Matrix Indicator (PMI) corresponding to the same partial channel is transmitted until the updated identification information is transmitted with the RI.
The method of claim 1,

The partial channel information includes a PCI (Partial CSI Indicator), channel state information transmission method.
A terminal for transmitting channel state information (CSI) in a wireless access system supporting massive MIMO (Massive) Multiple Input Multiple Output (MIMO),

RF (Radio Frequency) unit; And

Includes a processor,

The processor,

Receive CSI configuration information for CSI reporting,

And transmitting identification information on a partial channel corresponding to the CSI among all channels according to the CSI and the massive MIMO based on the CSI configuration information.
The method of claim 8,

When the identification information is the first value, the partial channel corresponds to the antenna of the first column of the antenna array according to the massive MIMO,

And when the identification information is the second value, the partial channel corresponds to the antenna of the first row of the antenna array according to the massive MIMO.
The method of claim 8,

The partial channel is associated with a single codebook when the identification information is a first value,

The partial channel is associated with a dual codebook when the identification information is a second value.
The method of claim 8,

When the identification information is the first value, the partial channel indicates that the ratio of the feedback frequency of the first partial channel and the second partial channel has a first ratio value,

And when the identification information is the second value, the partial channel indicates that the ratio of the feedback frequency of the first partial channel and the second partial channel has a second ratio value.
The method of claim 8,

The identification information is transmitted together with the CSI only when the CSI is a wideband PMI (Precoding Matrix Indicator), and is not transmitted together when the CSI is a narrowband PMI.
The method of claim 8,

The identification information is fed back with a RI (Rank Indicator), the terminal is transmitted, Precoding Matrix Indicator (PMI) corresponding to the same partial channel until the updated identification information is transmitted with the RI.
The method of claim 8,

The partial channel information includes a partial CSI indicator (PCI).